New file_size variable in file-link.html.twig

There's a new file_size variable in file-link.html.twig which can be used for displaying the size of the file. Currently, the size of the file is displayed with the link, but in Drupal 9 that will be up to the theme to decide whether they want to render the file size or not.

Before:

<span>{{ link }}</span>

After:

<span>{{ link }}</span>
{% if file_size %}
  <span>({{ file_size }})</span>
{% endif %}